1. Field of the Invention
The present invention relates to elevator door safety systems and, in particular, to a method and an apparatus for optically monitoring door interlocks in a hoistway.
2. Description of the Related Art
To prevent people from accidentally falling into an elevator shaft or hoistway of a building, as when an elevator door is opened and no elevator cab is positioned to receive passengers, safety systems must be employed to monitor the latch states of each door in the hoistway. Prior art safety systems utilize electrical contacts arranged to engage a conductive nosepiece of each door interlock device to sense the latch states of each door. The use of electric contacts requires precise alignment of the nosepiece. The electrical contacts experience wear from repeated contact engagement with the nosepiece. Therefore, periodic adjustments and maintenance of the nosepiece is required because of the significant wear which results from the door closing forces during use. The electrical contacts are subject to oxidation which may cause the electrical contacts to falsely report failures. In another failure mode, a broken conductor from the nose piece may lay across two contacts, thereby falsely reporting a latched state of the door.
Accordingly, there is a need for a safety system for monitoring the latch states of an elevator door in a hoistway, which overcomes the disadvantages of prior art systems.
An object of the present invention is to provide an apparatus for optically monitoring the latch states of an interlock device for an elevator door in a hoist way.
According to one aspect of the invention, a nosepiece of a door interlock device includes an optical input, an optical output, and an optical conduit disposed within the nosepiece for guiding an optical signal from the optical input to the optical output therethrough. The optical input and output are arranged at an angle from each other on the nosepiece so that the optical signal is transmitted therethrough only when the nosepiece is oriented within an acceptable level of tolerance with respect to corresponding optical input/output. In the preferred embodiment, the optical input is arranged perpendicular to the optical output.
According to another aspect of the invention, the nosepieces of a plurality of door interlock devices are connected in series between an optical transmitter and an optical receiver. When each of the door interlock devices is in a closed position or latched state, the receiver receives an optical signal from the optical transmitter. When one of the door interlock devices is in an open position or unlatched state, the receiver does not receive an optical signal from the transmitter.
In one embodiment, the elevator door is movable between a closed state and an open state. The inventive system includes a transmitter for emitting an optical signal and an interlock device for latching the elevator door when the elevator door is closed. The interlock device includes an optical nosepiece so positioned for receiving, guiding, and outputting the optical signal from the transmitter when the elevator door is closed and the interlock device is in the latched state. A receiver receives the optical signal from the nosepiece only when the elevator door is closed and the interlock device is latched to thereby indicate the elevator door is in its latched state.
Other objects and features of the present invention will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention, for which reference should be made to the appended claims. It should be further understood that the drawings are not necessarily drawn to scale and that, unless otherwise indicated, they are merely intended to conceptually illustrate the structures and procedures described herein.